Typically, a cassette which accommodates a plurality of substrates arranged in parallel is used when substrates are transported into and out of a substrate processing apparatus. Historically, in the case of a substrate processing apparatus which collectively takes out a plurality of substrates from a cassette to handle the substrates, a substrate transport robot of the substrate processing apparatus grasps and transports a plurality of substrates as one substrate group, with the pitch (spacing of arranged substrates) of the substrates which are received in the cassette maintained as it is.
FIG. 33 is a perspective view of parts of a substrate transport robot which hold substrates in a prior art substrate processing apparatus. In the substrate transport robot shown in FIG. 33(a), two rod-shaped members 635 are swingably provided to freely change the spacing therebetween. The two rod-shaped members 635 have grooves 635A cut at a predetermined pitch. The substrates are held by fitting the sides of the outer peripheries of the substrates to be transported into the grooves 635A while the spacing between the pair of rod-shaped members 635 is reduced.
On the other hand, the substrate transport robot shown in FIG. 33(b) includes two plate-shaped members 535 each of which is rotatable on a shaft 534. Each of the two plate-shaped members 535 has grooves 535A formed on opposite surfaces thereof at a predetermined pitch. The substrates are held by fitting the sides of the outer peripheries of the substrates to be transported into the grooves 535A while the pair of plate-shaped members 535 are rotated.
Therefore, the substrate transport robot shown in FIG. 33(a) has one area for holding the substrates, and the substrate transport robot shown in FIG. 33(b) has two such areas provided respectively in front and back surfaces of the plate-shaped members 535.
In a substrate processing apparatus which employs predetermined processing liquids stored in a plurality of processing baths to sequentially repeat the steps of dipping substrates in the processing liquids to perform a series of processes, the states of the substrates to be transported change in a step-by-step manner. When the substrate transport robot shown in FIG. 33(a), for example, is used in such a substrate processing apparatus, the substrates which have not yet been cleaned, the substrates being cleaned, and the substrates which have already been cleaned are held by the one area. Thus, for example, if the substrates transported into the apparatus are contaminated with particles and the like, the contamination is transferred to the substrates being cleaned or the cleaned substrates. Further, droplets of cleaning fluid deposited on the substrates being subjected to cleaning processing are sometimes deposited on the cleaned substrates. This results in the contamination of the substrates which have already been subjected to the cleaning processing to cause the problem of reduction in yield of the substrates in the cleaning processing.
The use of the substrate transport robot shown in FIG. 33(b) which has the two areas for holding the substrates slightly alleviates such a problem but still does not solve the problem of the contamination of the substrates which have already been subjected to the cleaning processing.
In some cases, it is desired to use a cassette having a pitch different from a conventional pitch in accordance with the number and types of substrates to be processed. However, since the pitch of the substrates that the substrate transport robot is capable of grasp is previously determined depending on the pitch of grooves cut in a grasping hand of the substrate transport robot, the use of the cassette having a different pitch requires the use of an apparatus designed specifically for pitch change. In this case, the size of the whole substrate processing apparatus increases, and the costs thereof also increase.
Further, cassettes actually have unnecessarily large substrate pitches, and the handling of the substrates with the pitches kept in this state might result in the increased size of the substrate processing apparatus or an insufficient throughput.
Then, in such a case, a technique has been used which employs, in addition to the substrate processing apparatus, an apparatus for changing the pitch of the substrates for handling of the substrates arranged at a pitch suitable for the substrate processing apparatus, wherein the substrates are once transferred to a specifically designed cassette that is capable of receiving therein the substrates at a smaller pitch and then the specifically designed cassette is transported into the substrate processing apparatus.
However, the above described technique wherein the substrates are transferred from the conventional cassette to the specifically designed cassette having the smaller pitch by using the pitch changing apparatus requires the transfer of the substrates in the pitch changing apparatus and the transport of the specifically designed cassette between the pitch changing apparatus and the substrate processing apparatus. This causes problems such as the generation and deposition of particles and the contamination of the substrates.
On the other hand, if the pitch changing apparatus is incorporated as it is into the substrate processing apparatus, another problem occurs that is the increased size of the substrate processing apparatus with the increase in space for handling of the specifically designed cassette. Additionally, in this case, it is necessary to make a controllable connection between the substrate processing apparatus and the pitch changing apparatus incorporated in the substrate processing apparatus.